At measurement of pH in solutions, strips made of litmus paper, for instance, are generally used, the strips being immersed into a solution to be measured, whereby the paper changes its colour in accordance with the environment, i.e. the pH value of the solution.
In principle, the above procedure functions at least in some situations, for instance in laboratory conditions. However, a problem is the difficulty and slowness of the measurement. In addition, the procedure is inconvenient for example in certain industrial conditions. Another drawback of the above technique is its one-time nature. At present, glass membrane sensors based on electrochemical phenomena are mainly used for pH measurement in the industry.